This invention relates to release agents used in various molding processes and textile manufacturing processes and methods for using these release agents. The release agents find use in molding/pressing lignocellulosic materials, casting concrete and molding polymer foams. The release agents also find use in textile handling equipment during manufacture.
One of the problems associated with pressing/molding processes, especially when processing wood, concrete and polyurethane foam, is that it is difficult for the articles formed of these materials to be released from the equipment used. It is well known in the art to employ release agents to aid in the removal of articles produced from the manufacturing equipment used. Examples of release agents include oils, wax, polishes, metallic salts, silicones and polytetrafluoroethylene. Release agents have been applied to molding/pressing equipment such as press platens and they also have been applied to the materials to be processed. The following patents are representative of the art of release agents:
U.S. Pat. No. 4,257,995 issued to McLaughlin et al.;
U.S. Pat. No. 4,257,996 issued to Farrissey, Jr. et al. on Mar. 24, 1981;
U.S. Pat. No. 4,609,570 issued to Couleau et al. on Sep. 3, 1986;
U.S. Pat. No. 5,908,496 issued to Singule et al. on Jun. 1, 1999;
U.S. Pat. No. 5,194,584 issued to Leahy on Mar. 16, 1993;
U.S. Pat. No. 5,942,058, issued to Sleeter et al. on Aug. 24, 1999;
U.S. Pat. No. 6,132,503 issued to Singule et al. on Oct. 17, 2000;
U.S. Pat. No. 6,231,656 issued to Dekerf et al. on May 15, 2001;
EP 46014, and
EP 57502.
Release agents are especially useful when molding lignocellulosic materials such as wood sheets, chips, fibers, flakes, strands, etc., into composite structures with polyisocyanate adhesives. Certain agents are used internally, i.e., as an emulsion or mixture with the polyisocyanate adhesive and others are applied externally, i.e., applied to the metal surfaces of the press platens and/or the lignocellulosic material itself. In typical molding processes, lignocellulosic materials of a desired size and shape are prepped and coated with an adhesive comprised of a polyisocyanate or phenolic resin (urea formaldehyde, phenol-formaldehyde, melamine urea formaldehyde, and melamine formaldehyde resins.). Polyisocyanate binders have been favored over phenolic resins in binding certain lignocellulosic materials. The adhesive coated lignocellulosic materials are loaded into a press where heat and pressure are applied simultaneously in order to compress the lignocellulosic material to a desired thickness and activate the adhesive. The lignocellulosic material is then bonded to form the desired composite product. Examples of composite products comprised of lignocellulosic materials include: particle board, oriented strand board (OSB), plywood, chip board, medium density fiber board (MDF), hardboard, and structural strand lumber.
A suitable release agent remains free flowing within the intended use temperatures and should be shelf stable for extended periods. In selecting a release agent, it is desirable that the agent not only have the properties necessary to provide adequate release of the article produced from the equipment employed, but it should be non-staining, i.e., it should not discolor the products. For example, tall oil fatty acids have been used as release agents for lignocellulosic materials but suffer from discoloring the molded articles formed. It is desirable for the release agent not to discolor the molded article to reduce finishing. In the case of oriented strand board, it is desirable to eliminate the need to sand the panel except to achieve caliper.
Certain release agents can also lead to considerable build up of wax, rosin or other deposit forming material on the equipment used, which is undesirable. It is desirable to reduce, preferably eliminate, these deposits on the equipment utilized.
Preferably, the release agent is non-corrosive to the molded produced and the equipment employed. It is desirable that the release agent minimizes the corrosive effects of water, acids and other aggressive agents in preparing molded articles.
It is also desirable to minimize ambient air odor or VOC when spraying the release agent to avoid environmental hazards in its use, storage and disposal and to improve productivity.
Another feature desired is to increase the memory of a release agent. This is defined herein as the ability of a release agent to perform its function after unscheduled equipment shut down and after the release agent has been applied. This allows the line to start up again without dumping a portion of the web or re-wetting the web with more release agent. This allows for downtime during the manufacturing process with few, and preferably no additional steps necessary to restart the process.
It is also desirable to enhance the release properties of a release agent so that less is required, thereby reducing the cost of manufacturing.
There is a continuing effort to provide release agents with a better balance of these properties.